Table-tennis ball throwing machine using air propulsion

ABSTRACT

A pneumatic ball propelling device to be used in practicing table tennis is mounted on a separate table near the corner of a playing table. A tube from which balls are propelled one at a time at predetermined intervals has an inlet connected to the outlet of a house-hold vacuum cleaner and an intermediate chute extending upwardly to a receptacle for holding a supply of balls. A gate comprising a notched disk, such as a notched playing record, in the bottom of the receptacle is rotated to release a ball carried within a notch of the disk as the notch passes over the top of the chute. The outer end of the tube has a long strip of resilient material including an outer layer of rubber and an inner layer of plastic foam along its inner wall to impart spin to a ball being delivered. The outer end is rotatably adjustable to control direction of spin and telescopically adjustable to control the path of the ball.

1 Nov. 12, 1974 1 1 TABLE-TENNIS BALL THROWING MACHINE USING AIR PROPULSION [76] Inventor: Milton C. Schatz, 209 N. Fifth St.,

Eldridge, Iowa 52748 22 Filed: Sept. 17, 1973 21 Appl. No.: 397,695

Related US. Application Data [63] Continuation-in-part of Ser. No. 204,096, Dec 2,

1971, abandoned.

[52] U.S. Cl. 124/11 R, 124/30 R, 124/50, 124/51 R, 273/30 [51] Int. Cl F411 1/04 [58] Field of Search 124/11 R, 30 R, 50, 51 R; 273/26 D, 30, 58 R, 58 A, 58 B, 58 BA, 273/DIG. 5, DIG. 8

3,521,617 7/1970 Heinz 124/50 X 3,584,614 6/1971 Horvath 124/11 R 3,680,540 8/1972 Stengl 124/11 R Primary Examiner-Richard C. Pinkham Assistant Examiner-R. T. Stouffer Attorney, Agent, or FirmHenderson & Strom [57] ABSTRACT A pneumatic ball propelling device to be used in practicing table tennis is mounted on a separate table near the comer of a playing table. A tube from which balls are propelled one at a time at predetermined intervals has an inlet connected to the outlet of a house-hold vacuum cleaner and an intermediate chute extending upwardly to a receptacle for holding a supply of balls. A gate comprising a notched disk, such as a notched playing record, in the bottom of the receptacle is rotated to release a ball carried within a notch of the disk as the notch passes over the top of the chute. The outer end of the tube has a long strip of resilient material including an outer layer of rubber and an inner layer of plastic foam along its inner wall to impart spin to a ball being delivered. The outer end is rotatably adjustable to control direction of spin and telescopically adjustable to control the path of the ball.

6 Claims, 7 Drawing Figures wimznnumm 3.847.132 sum 20? 3 INVENTOR. MILTON C. SCHATZ TABLE-TENNIS BALL THROWING MACHINE USING AIR PROPULSION CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application Ser. No. 204,096, filed Dec. 2, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to games and particularly to devices for throwing balls across the net of table tennis to enable a player to practice alone.

A device using a spring-loaded plunger to throw balls from a tube is shown in U.S. Pat. No. 2,199,009 issued to G. H. Perryman on Apr. 30, 1940. The outlet of the tube has an adjustable spin control comprising a rubber band. In addition to a plunger that propels the balls, a plunger is used at a lower level to feed the balls upwardly to the propelling tube. The balls are returned to the lower plunger by gravity from one of the playing table to which the ball-throwing device is attached.

Rotating vanes for producing a flow of air to propel ping-pong balls is shown in U.S. Pat. No. 2,765,171 issued to Jay E. Cook on Oct. 2, 1956. Balls hit by a player are returned to the ball-throwing device by troughs that extend along the sides of one end of the table, and then the balls are thrown from a tube that extends nearly to the net extending in a usual manner across the center of the table. Balls are fed one at a time to the bottom of the tube by a deflector plate that has a hole to be aligned with an inlet hole near the rotating vanes.

An air flow system utilizing a household vacuum cleaner for propelling Ping-pong balls is shown in U.S. Pat. No. 2,508,461 issued to G. Lemon on May 23, 1950. A box structure resembling a large funnel is mounted along the lower portion of a screen that is a stop for balls that have been hit by a player. The lower portion of the funnel is directed to an opening in the wall of a hose having a lower end connected to the blower outlet of a vacuum cleaner and an upper end curved up over one end of the table above the screen to propel balls from the tube toward the other end of the table. A ball returned by a player to the screen falls in the funnel and continues without stopping to the propelling tube.

SUMMARY OF THE INVENTION An object of this invention is to provide an inexpensive ball-throwing apparatus to propel successively at predetermined times a plurality of table-tennis balls from a position beyond the end of a playing table and to impart to the propelled balls a selected direction of spin. A feature of the apparatus is the provision for determining the amount of variation in the curve of the path of successively thrown balls, and another feature is the provision for displaying each of the balls just before it is put in play to signal a player to be ready to return the ball.

A tube with a diameter gennerally somewhat greater than the diameter of a tennis ball has one end adapted to receive the nozzle of an air-blowing device and the other end for receiving a telescoping tube for determining trajectory and spin of the balls that are propelled therefrom by air flow. The amount by which the telescoping tube is extended determines variation in trajectory of successively thrown balls, and its rotative position determines the direction of spin. The spin is developed by the ball contacting a long resilient strip attached longitudinally along the inside wall of the telescoping tube, the friction between the ball and the strip being greater than that between the ball and the smooth wall of the tube.

The balls to be played are placed in a receptacle supported above the propelling tube and are fed by gravity one at a time through a mechanical gate from the bottom of the receptacle. A tubular chute extends slanlingly downwardly from the bottom of the receptacle and joins the ball-propelling tube a short distance from its air inlet to introduce the ball to the tube with a component of motion in the direction of the air tlow in the tube. The bottom of the receptacle includes a rotatable disk as the gate with a notch in its edge for moving the balls one at a time to the top of the chute, and as the notch passes over the top of the chute, the ball is released to fall through the chute to the propelling tube. The chute has an opening or window facing the player,

and the appearance of the ball as it falls past the window signals the player that a ball is about to be put in play. Preferably, the ball-throwing apparatus is mounted on a separate table placed in a diagonal direction a short distance from a playing table.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an oblique top view of the ball-throwing ap paratus of this invention mounted on a small table positioned near a playing table;

FIG. 2 is a cross-sectional view of the ball-throwing apparatus taken on a vertical plane that bisects its receptacle and its ball-propelling tube;

FIG. 3 is a top perspective view of the receptacle and -ball dispensing device of the ball-throwing apparatus;

'FIG. 4 is a front plan view of the ball-throwing apparatus;

FIG. 5 is a diametral cross section of the outer end of the telescoping tube from which balls are propelled;

FIG. 6 is an oblique view of an air-flow restricting device that is adapted to be inserted in a slot of the ballpropelling tube; and

FIG. 7 is an enlarged, forshortened cross-sectional view of the entrance end of the propelling tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the pneumatic ballthrowing assembly includes a base 12 upon which is mounted a ball-storage receptacle 13 above a ballpropelling tube 14. The assembly 11 is mounted on a small table, conveniently a card table, spaced in a diagonal direction from a corner of a playing table 16. The table 15 is positioned to put in play table-tennis balls successively from the ball-propelling tube 14 over the adjacent corner of the table 16. The halls are thrown over the usual net that is placed across the center of the table and toward the player who desires to practice returning the balls to the end of the table adjacent the ball-throwing assembly 11. A blanket or net 17 is hung just back of that end of the table to which the balls are being returned, and the lower end of the blanket is folded loosely and fastened to the underside of the end of the table to provide a fold 18 in which the returned balls are collected. After all of the balls have been put in play by the assembly 11, and the player has shut the device off as described below, the balls are collected from the fold and placed back in the receptacle 13.

The source of power for propelling the ball may be conveniently a household tank-type vacuum cleaner 19 with its blower outlet connected through its hose to the inlet of the ball-propelling tube 14. As shown in FIG. 2, the tube 14 has an inlet 22 in which the nozzle of the hose 22 fits tightly. The inside of the tube is smooth and has a diameter sufficient to receive a spin control tube as described below with a diameter of approximately 1% inches for passing 1 /2-inch tennis-table balls. The tube 14 is mounted on the base 12 such that the end of the tube from which the ball is propelled is slanting somewhat upwardly. The tube 14 is held in position by the chute 24 that extends upwardly and has the upper end secured to the bottom of the receptacle 13 just inside the outer circumference of the main portion of the receptacle. The chute 24 joins the ballpropelling tube 14 a short distance from the inlet 22 to make an acute angle with the inlet portion of the tube such that a ball that falls through the chute 24 has a component of motion as it enters the tube 14 in the direction of the air flow toward the outlet of the tube.

Except for a notched portion 26, a rotatable disk 25 (F108. 2 and 3) covers the bottom of the receptacle 13. The width of the notch 26 in the direction of the diameter of the disk is slightly greater than the diameter of a table-tennis ball, and the width along the circumference of the disk is about l /z times the diameter of a ball. in a model of the ball-propelling apparatus 11, the disk 25 is a phonograph record on a player mechanism that includes an electric motor 27 connected in a usual manner to a turntable on which the record is placed. The record-playing mechanism is adjustable to rotate the disk 25 at a speed of either 33% or 45 revolutions per minute. When the disk 25 contains only one notch 26, one of these speeds of rotation can be selected to supply balls from the receptacle 13 at desired intervals for practicing. A container 13 has a stationary bottom 28 at a distance equal to approximately one-half the diameter of a table tennis ball below the disk 25. The bottom 28 must provide an unbroken surface beneath the notch 26 to support a ball in the notch as it travels within the main vertical wall of the receptacle 13 and then beneath an inwardly curved portion 31 out of the main portion of the receptacle to the top of the chute 24.

As shown in FIG. 4, the receptacle 13 and the disk 25 are tipped sufficiently on the base 12 to position the balls at the edge of the disk so as long as any balls are in the receptacle 13, a ball will be in a position to drop into the notch 26 of the disk 25 during each revolution. Looking at the receptacle 13 from the direction facing the outlet of the ball-propelling tube 14, the legs 29 on the left are shorter than the legs 30 on the right for sup porting the receptacle 13 above the base 12. The balls that are to be delivered therefore tend to roll to the edge of the disk to the position where the notch 26 will move under them shortly after it has moved clockwise past the top of the chute 26 as viewed from above.

The cylindrical shape of the vertical wall of the receptacle 13 is modified by an inwardly curved portion 31 that extends toward the center of the receptacle to exclude the top of the chute 24 from the main part of the receptacle. A curved guide strip 32 extends horizontally from a point on'the outer wall of the container 13 clockwise to an intermediate point on the curved portion 31 of the wall, and a stop strip 34 continues clockwise in the direction of the circumference of the main wall of the receptacle 13 beneath the inwardly curved portion 31 until the end of the strip is curved inwardly over that portion of the upper edge of the chute 24 that is passed over last by the notch 26 as it is rotated clockwise. Vertically, the strip 34 is even with the ball 33 that is being moved in the notch 26 to guide the ball 33 to the position over the chute 24 and the curved end of the strip is placed to function as a stop to prevent the ball from being carried over the top of the chute. Most of the lower edge of the inwardly curved portion 31 of the vertical wall of the container 13 is spaced a short distance above the upper surface of the disk 25, but a notched portion 44 under which the notch 26 passes beyond guide strip 32 is at a distance somewhat greater than fa the diameter of a table-tennis ball above the surface of the disk to permit a ball being moved in the notch along the bottom 28 to pass under the wall from the main portion of the container. Likewise, the lower edge of the guide strip 32 is at about the same height to allow a ball in the notch 26 to pass under it and to act as a guide for other balls that are being carried around on the upper surface of the disk to divert them gradually to the lowest portion of the edge of the disk. The disk 25 operates to deliver the balls one at a time under the guide strip 32 to the chute 24 without jamming and without damaging the balls.

With reference to FIG. 4, in order to signal a player that a ball is to be delivered, the chute 24 has a window 35 a short distance from the top of the chute and facing the player. As the ball 33 is fed to the top of the chute 24 from the notch 26 of the disk 25, its appearance as it passes the window 35 signals the player that the ball is about to be delivered.

The complete tubular assembly for propelling the table-tennis balls by air includes a delivery and spincontrol tube 36 telescopically fitted to the outlet of the ball-propelling tube 14. By pulling outwardly on the dclivery tube 36 such as to increase the overall length of the ball-propelling assembly, the curves of the paths of the successively-thrown balls vary less than when the ball-propelling assembly is shortened by pushing inwardly on the delivery tube 36.

The delivery tube 36 is preferably made from plastic material and has an inside diameter of approximately 1% inches. One end 49 is notched to facilitate placing that end within ball-propelling tube 14 that has somewhat larger diameter. The tube 36 is held in position by a clamp 23 that includes a pair of parallel straps 45 and 46 spaced apart a distance equal to approximately the outside diameter of the tube 36 and extending upwardly from the base 12 a sufficient distance to hold the tube 36 between them in line with the ballpropelling tube 14. The amount of clamping force on the tube 36 is adjusted by a wing nut 48 on a bolt 47 extending horizontally through the upper ends of the straps 45 and 46.

Spin is imparted to the ball by a strip of rubber 37 (FlGS. 2 and 5), beveled at 37a (FIG. 7) to aid entry of the ball, and an underlying strip of resilient plastic foam or rubber foam 38 positioned longitudinally along the inner wall of the outward end of the delivery tube 36. The combined thickness of the strips is sufficient to and obviously, the friction between the rubber strip 37 and the ball is greater than the friction between the ball and the opposite portion of the wall of the delivery tube. A desired amount of friction is supplied by using electrical rubber tape for the rubber strip 37 with the smoother side facing the interior of the tube 36.

Referring specifically to FIG. 7, it can be seen that the bevel 37a is formed by the strip 37 being tightly secured at the entrance end of the tube 36. Furthermore, a thin strip 51 of plastic tape can be secured to the exterior of the tube 36 in an overlapping manner, then adhered to the strip 37 over the bevel area 37a for a protection. It has been found that the provision of the foam 38 functions as an air cushion relative to passage of the balls 33 through the tube 36, aiding their propulsion. The tube 36 is rotated to different positions to control the direction of spin. When the rubber strip 37 is at the top of the tube as shown in FIGS. 2 and 5, underspin or chop will be produced, and if the tube 36 is rotated /2 turn to place the rubber strip 37 in the lowest position in the tube, topspin will be produced. The delivery tube 36 can be rotated in any position between the positions for producing topspin and underspin to produced any degree of sidespin. The wing nut 48 is loosened slightly while the tube is rotated and tightened to hold the tube in the position to which it has been adjusted. The tube can also be moved slightly in a vertical direction in the clamp 23 to vary slightly the angle at which the balls are propelled toward the playing table.

A speed control is provided on the ball-throwing apparatus to enable a player to select a speed that closely simulates the speed for different types of plays between two players. Usually the ball-throwing apparatus is adjusted to deliver balls to which an underspin has been applied at a slower speed than the balls to which topspin has been applied. When the blower or vacuum cleaner 19 does not have a satisfactory air-flow control device, the delivery tube 36 can be extended to let air flow from notches of the notched end 49 or an airrestricting device 39 as shown in FIG. 6 can be used. The restricting device is adapted to fit in a slot 43 in the wall of the ball-propelling tube 14 a short distance from the inlet 22. The air-restricting device comprises a cap 40 curved to fit the exterior surface of the ballpropelling tube 14, a handle 41 projecting upwardly from the cap, and one or more tines projecting downwardly to extend across the ball-propelling tube 14 when the device 39 is inserted in the slot 43. With properly spaced tines 42 for the air blower 19 that is being used and with the air-restricting device 39 in the slot 43, a desired slower speed for practicing with balls having underspin is provided. I

To prepare for practicing, the ball-throwing device 11 is placed on a small table and is positioned such that the delivery tube 36 delivers the balls in a diagonal direction over one of the corners of the table remote from the player who desires to practice. The telescoping tube 36 is adjusted inwardly or outwardly to provide a desired amount of variation in the paths of succeeding balls, and it is rotated to position the rubber strip 37 to provide a desired direction of spin. If a relatively slow delivery is desired, the speed control 39 of FIG. 6 is inserted in the slot 43 of the ball-propelling tube I4. A mechanical or remote control switch (not shown) is provided for controlling the motor 27 of FIG.

7 press the rubber strip 37 lightly against a passing ball,

2. When the player is ready to practice, he starts the blower l9 and by using remote control, he starts the motor 27 for rotating the disk 25. Table-tennis balls are released periodically by the rotating disk 25 to be passed through the chute 24 to the ball-propelling tube 14. As each ball travels downwardly in the chute 24, it can be seen through the window 35 of FIG. 4 to signal the player that the ball is to be delivered. The speed of rotation of the disk 25 can be conveniently selected to rotate the disk at either 33 /3 or 45 revolutions per minute. At a slower speed, the intervals between successive balls are about as long as the usual player would desire; and at the higher speed, the intervals are about as short as the usual player would desire. After the supply of balls has been served from the receptacle 13, the player shuts off the motor 27, scoops the balls from the fold 18 of the blanket l7 and returns them to the receptacle 13 in preparation for additional practicing. While the ball-throwing device 11 is not in use, it can be made more compact by loosening the wing nut 48 of the clamp 23 and removing the delivery tube 36.

I claim: 1. A pneumatic ball-throwing machine comprising: a ball-propelling tube, one end of said tube being an inlet adapted to be attached to an air-blowing device, the other end of said tube being an outlet pointed in the direction balls are to be thrown, a chute through which balls are to be supplied to said outlet, said chute joining said propelling tube at a point intermediate its ends, a receptacle for balls mounted above said ball-propelling tube, said chute extending from said propelling tube upwardly to an outlet in the bottom of said receptacle, mechanical gating means in the outlet of said receptacle operable repeatedly to permit balls to fall one at a time from said receptacle to said ballpropelling tube, said mechanical gating means comprising a notched disk, the continuous portion of the edge of said disk extending across said outlet of said receptacle, the edge of said disk having at least one notch, the width of said notch in the circumferential direction of said disk being greater than the diameter of the balls to be served and the depth of the notch from the edge of the disk being sufficient to allow a ball to pass to said chute while said notch is across said outlet of the receptacle, and means for rotating said disk at a predetermined rate to feed balls from said receptacle to said chute at desired intervals. 2. A pneumatic ball-throwing machine as claimed in claim 1 wherein said receptacle is a substantially cylindrical container, said disk fitting as a bottom within the vertical cylindrical wall of said container to support a supply of balls, a lower bottom portion extending below the path subscribed by said notch as said'disk is rotated, the distance between said disk and said lower bottom portion being equal to a substantial fraction of the diameter of each of said balls so that a ball contained with said notch is carried on said lower bottom portion to said outlet of said receptacle, a guide strip positioned at a distance less than the diameter of the balls above said disk and extending from said vertical wall about said outlet of said receptacle to exclude from said outlet the balls within said container except the ball within said notch being carried on said lower bottom portion below said guide strips.

3. A pneumatic ball-throwing machine as claimed in claim 2 having a stop strip extending from the wall of said container across the path of a ball being carried in said notch by said disk, said stop strip being located over a portion of the wall of said chute to prevent said ball from passing over said chute and to guide: said ball downwardly into the chute.

4. A pneumatic ball-throwing machine as claimed in claim 3 wherein said inlet portion of said ballpropelling tube has an air flow control comprising an elongated member and means for selectively positioning said member across said inlet portion.

5. A pneumatic ball-throwing machine as claimed in claim 2 in which mounting means supports the bottom of said cylindrical container in a tilted position such that balls remaining in the container tend to roll to a position where said notch is located after it has passed over said chute and made a part of a revolution.

6. A pneumatic ball-throwing machine comprising: an adjustable delivery tube, one end of said tube being an inlet adapted to be attached to an air-blowing device, the other end of said tube being an outlet pointed in the direction balls are to be thrown, a chute through which balls are to be supplied to said outlet, the chute joining said adjustable delivery tube at a point intermediate its ends, a receptacle for balls mounted above said adjustable delivery tube, said chute extending from said adjustable delivery tube upwardly to an outlet in the bottom of said receptacle, mechanical gating means in the outlet of said receptacle operable repeatedly to permit balls to fall one at a time from said receptacle to said adjustable delivery tube,

said adjustable delivery tube having a coaxial strip along its inner wall, said strip comprising at least two layers of material having different resilient and surface friction characteristics, the one of said layers of material closest to the wall being relatively soft and easy to compress to function as an air cushion, the other one of said layers of material having a generally closed surface facing inwardly toward the center of the tube for contacting a passing ball, said other layer of material having surface friction substantially greater than that of the inside surface of said delivery tube, and said delivery tube being rotatably adjustable to provide different desired directions of spin to a ball being delivered from the outlet of said delivery tube, and further wherein said one layer of resilient material closest to the wall of said delivery tube is plastic foam and the other of said layers of resilient material is a separate strip of rubber tape.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,8h7,132

DATED 1 Nov. 1?, 1 7 t INVENTOR(S) Milton 0. Schatz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 1, on line 25, the word pi1 1g-pong should read -Ping-pong-.

Signed and Scaled this ninth D ay 0F September 1975 [SEAL] A Itesr:

RUTH. C. M A SON C MARSHALL DANN Arresting Officer (ummr'sxl'mrcr oflalenls and Trademarks 

1. A pneumatic ball-throwing machine comprising: a ball-propelling tube, one end of said tube being an inlet adapted to be attached to an air-blowing device, the other end of said tube being an outlet pointed in the direction balls are to be thrown, a chute through which balls are to be supplied to said outlet, said chute joining said propelling tube at a point intermediate its ends, a receptacle for balls mounted above said ball-propelling tube, said chute extending from said propelling tube upwardly to an outlet in the bottom of said receptacle, mechanical gating means in the outlet of said receptacle operable repeatedly to permit balls to fall one at a time from said receptacle to said ball-propelling tube, said mechanical gating means comprising a notched disk, the continuous portion of the edge of said disk extending across said outlet of said receptacle, the edge of said disk having at least one notch, the width of said notch in the circumferential direction of said disk being greater than the diameter of the balls to be served and the depth of the notch from the edge of the disk being sufficient to allow a ball to pass to said chute while said notch is across said outlet of the receptacle, and means for rotating said disk at a predetermined rate to feed balls from said receptacle to said chute at desired intervals.
 2. A pneumatic ball-throwing machine as claimed in claim 1 wherein said receptacle is a substantially cylindrical container, said disk fitting as a bottom within the vertical cylindrical wall of said container to support a supply of balls, a lower bottom portion extending below the path subscribed by said notch as said disk is rotated, the distance between said disk and said lower bottom portion being equal to a substantial fraction of the diameter of each of said balls so that a ball contained with said notch is carried on said lower bottom portion to said outlet of said receptacle, a guide strip positioned at a distance less than the diameter of the balls above said disk and extending from said vertical wall about said outlet of said receptacle to exclude from said outlet the balls within said container except the ball within said notch being carried on said lower bottom portion below said guide strips.
 3. A pneumatic ball-throwing machine as claimed in claim 2 having a stop strip extending from the wall of said container across the path of a ball being carried in said notch by said disk, said stop strip being located over a portion of the wall of said chute to prevent said ball from passing over said chute and to guide said ball downwardly into the chute.
 4. A pneumatic ball-throwing machine as claimed in claim 3 wherein said inlet portion of said ball-propelling tube has an air flow control comprising an elongated member and means for selectively positioning said member across said inlet portion.
 5. A pneumatic ball-throwing machine as claimed in claim 2 in which mounting means supports the bottom of said cylindrical container in a tilted position such that balls remaining in the container tend to roll to a position where said notch is located after it has passed over said chute and made a part of a revolution.
 6. A pneumatic ball-throwing machine comprising: an adjustable delivery tube, one end of said tube being an inlet adapted to be attached to an air-blowing device, the other end of said tube being an outlet pointed in the direction balls are to be thrown, a chute through which balls are to be supplied to said outlet, the chute joining said adjustable delivery tube at a point intermediate its ends, a receptacle for balls mounted above said adjustable delivery tube, said chute extending from said adjustable delivery tube upwardly to an outlet in the bottom of said receptacle, mechanical gating means in the outlet of said receptacle operable repeatedly to permit balls to fall one at a time from said receptacle to said adjustable delivery tube, said adjustable delivery tube having a coaxial strip along its inner wall, said strip comprising at least two layers of material having different resilient and surface friction characteristics, the one of said layers of material closest to the wall being relatively soft and easy to compress to function as an air cushion, the other one of said layers of material having a generally closed surface facing inwardly toward the center of the tube for contacting a passing ball, said other layer of material having surface friction substantially greater than that of the inside surface of said delivery tube, and said delivery tube being rotatably adjustable to provide different desired directions of spin to a ball being delivered from the outlet of said delivery tube, and further wherein said one layer of resilient material closest to the wall of said delivery tube is plastic foam and the other of said layers of resilient material is a separate strip of rubber tape. 